1. Field of the Invention
The invention is related to the field of powder metalurgy and in particular to a method for inducing superplastic properties in metals and alloys which have no superplastic properties.
2. Prior Art
Superplasticity is a property of certain alloys that allows them to be extensively deformed under appropriate conditions with very little stress. The prerequisite of superplastic alloys are defined by J. Wadsworth, T. Oyama and O. Sherby in their presentation "Superplasticity--Prerequisites and Phenomenology" at the Inter-American Conference on Materials Technology, Aug. 12-15, 1980, San Francisco, California, and by H. W. Hayden, R. C. Gibson and J. H. Broply in their article, "The Relationship Between Superplasticity and Formability", Metalurgical Society AIME, Plenum Press, 1971, pp. 475-497. Accordingly, for an alloy to exhibit superplasticity it should be of microduplex structure having a grain size of less than 10 micrometers, be either a eutectic or eutectoid composition, having a high strain rate sensitivity of flow stress and high angle grain boundaries.
A typical superplastic alloy is the nickel based alloy disclosed by Frecke et al in U.S. Pat. Nos. 3,702,791 and 3,775,101. Other superplastic alloys are described in the articles by J. Wadsworth et al and H. W. Hayden et al cited above.
Marya and Wyon, Proceedings of the 4th International Conference on the Strength of Metals and Alloys, Nancy France, Vol. 1, 1976, pp. 438-442 and Weill and Wyon, Proceedings of the 5th International Conference on the Strength of Metals and Alloys, Aachen, W. Germany, Vol. 1, 1979, pp. 387-392, have succeeded in making fine grained aluminum-gallium alloys superplastic at 50.degree. C. by rubbing gallium on an aluminum surface and heat soaking the wetted aluminum at 50.degree. C. for up to 50 hours. The invention is an alternative method for inducing superplastic properties in nonsuperplastic metal and alloy powders.